Mechanical strains within a semiconductor device substrate can modulate device performance by, for example, increasing the mobility of the carriers in the semiconductor device. That is, strains within a semiconductor device are known to enhance semiconductor device characteristics. Thus, to improve the characteristics of a semiconductor device, tensile and/or compressive strains are created in the channel of the n-type devices (e.g., NFETs) and/or p-type devices (e.g., PFETs), respectively. However, the same strain component, for example tensile strain or compressive strain, improves the device characteristics of one type of device (i.e., n-type device or p-type device) while discriminatively affecting the characteristics of the other type device.
Accordingly, in order to maximize the performance of both NFETs and PFETs within integrated circuit (IC) devices, the strain components should be engineered and applied differently for NFETs and PFETs. That is, because the type of strain which is beneficial for the performance of an NFET is generally disadvantageous for the performance of the PFET. More particularly, when a device is in tension (in the direction of current flow in a planar device), the performance characteristics of the NFET are enhanced while the performance characteristics of the PFET are diminished.
To selectively create tensile strain in an NFET and compressive strain in a PFET, distinctive processes and different combinations of materials are used. For example, it is known to place stressor materials such as, for example, SiGe and/or Si:C in the source and drain regions of the FET to selectively induce appropriate strain in the channels of the FET devices. Another example is the use of liners on gate sidewalls to selectively induce the appropriate strain in the channels of the FET devices. The level of strain that can be applied in the latter situation is typically moderate (i.e., on the order of 100s of MPa). However, strain can be limited by the rigid gate material. More specifically, polysilicon with a high Young's Modules, e.g., upwards of 200 Gpa, effectively restricts the strain component provided by the stressor materials. That is, the rigid polysilicon will oppose relaxation of the stressor materials thereby restricting the channel strain.
Thus, it is desired to provide more cost-effective and simplified methods for creating larger tensile and compressive strains in the channels of the NFETs and PFETs, respectively. Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.